Methods and apparatus for the wireless control of lift devices by infrared transmission are known. For example, European Unexamined Patent Application No. EP O 195 665 A2 discloses a device for the wireless control of an apparatus, and in particular through infrared transmission of control signals for the control of cranes. Specifically, the prior art control device includes a transmitting unit and a receiving unit. The transmitting unit consists essentially of function-selecting switch elements, a coder, for encoding the selected commands of the switch elements, and infrared diodes for transmitting the coded infrared signals from the transmitting unit. The infrared signals sent by the transmitting unit are received by sensors located in the receiving unit. The received signal is then decoded in a decoder and is used to control the electric loads of the crane.
In order to insure reliable operation in controlling the crane, the transmitting and receiving units continue to communicate via continuously or periodically transmitted infrared signals such that a control signal is continuously transmitted as the crane is operated. Thus, upon actuation of a switch element in the transmitting unit, a function signal corresponding to the selected crane function is sent out as an infrared signal. An interruption of the periodically or continuously transmitted function or control signal for more than a predetermined interval during operation of the crane, causes a shutdown of all crane functions. For example, a failure in the electronic system or exceeding of the range of the transmitting unit so that the receiver no longer receives the repeated-transmitted control signal leads to such a shutdown of all crane functions.
However, this prior art device has serious disadvantageous when used by several operators since the transmitting unit, which is implemented as a held transmitter, must be transported and physically handed over to the next operator, with a consequent loss of time both by the operator and of the crane's availability to perform the operations for which it is needed.